Rough running at low rpm + lazy tachometer.

[Unrest]

I'm new to this forum, so please bear with me if this problem has been debated before.

I recently bought a '94 AT with a couple of problems included at no extra cost.

At low rpm, the engine runs roughly and seems to misfire or "choke", but when the engine revs up, the bike suddenly jerks forward like crazy and runs quite normally from there up to higher rpms. The tachometer needle won't climb above 3000 rpm no matter how fast the engine runs, though.

Does anyone here have a suggestion as to where I might look for a solution? Is there a connection between the engine/running problem and the tacho symptoms?

Any suggestion is greatly appreciated!

[BIGROG]

Welcome to XRV.

Without seeing the bike the first thing that springs to mind is what happend to my RD07A, check the choke cables are not stuck and holding one or both plunges out in the carbs and over fueling the bike (a very common fault). As for the tacho, I have had a few Honda's with lazy tacho's, you can check by replacing with a known good one or use an avometer or motormeter if you have one but make sure it it set to read the correct range or you will damage your electrical system.
Good luck and I am sure others will come up with more help shortly.

Rog

[FatFergie]

Could be your ignition control box (aka CDI).

[AlanH]

The tacho fault is likely to have been caused by a failure in the regulator rectifier at some point which may have been replaced in the past. When the reg/rect goes and the bike overcharges, it can kill the tacho.

The rough low rpm running could be a number of things from tight clearances or muck in the carburettors to sticky choke plungers/cable. It's most likely not coils or CDI as these tend to either break down at higher rpm or just not work at all.

For the rough running I'd start with the carbs and strip and clean them. While they are out of the way, I'd do the valve clearances, change the plugs and also check the inlet rubbers.

The faults are probably not related.

[StumpyFingers]

Also check the carbs a balanced.
If the pilot screws are wrong I believe they should both be two and a half turns out. I would not run on both cylinders until it goes to main jets.

[Larry Biskit]

Try to get it running right first and see if that brings the tacho into line. Could be an airleak somewhere around the carbs... maybe the previous owner had fittings for scott oiler between carb and engine, that are not connected or leaking. Check your airfilter is clean too, or just get a new one. Have a good look from the outside before you pull all apart. Heavily likely its a choke issue. Theres a fix for the tacho, depending on what model it is. Let us know how you get on. Good luck.

[Unrest]

Thanks for the feedback!
Looks like I have my weekend carved out. I'll try to work my way through the easier and more obvious stuff first, and then move on to the choke and carburettor issues. I'll post about the progress...